gunzip: fix incorrect decoding of "fixed" inflate blocks

function                                             old     new   delta
huft_build                                          1008    1022     +14
inflate_block                                       1253    1256      +3
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 17/0)               Total: 17 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 20 insertions, 10 deletions

diff --git a/archival/libarchive/decompress_gunzip.c b/archival/libarchive/decompress_gunzip.c
index 0f8173d0a..03049cc9b 100644
--- a/archival/libarchive/decompress_gunzip.c
+++ b/archival/libarchive/decompress_gunzip.c
@@ -280,11 +280,17 @@ static unsigned fill_bitbuffer(STATE_PARAM unsigned bitbuffer, unsigned *current
  * b:   code lengths in bits (all assumed <= BMAX)
  * n:   number of codes (assumed <= N_MAX)
  * s:   number of simple-valued codes (0..s-1)
- * d:   list of base values for non-simple codes
- * e:   list of extra bits for non-simple codes
+ * cp_ext->cp,ext: list of base values/extra bits for non-simple codes
  * m:   maximum lookup bits, returns actual
  * result: starting table
+ *
+ * On error, returns a value with lowest-bit set on error.
+ * It can be just the value of 0x1,
+ * or a valid pointer to a Huffman table, ORed with 0x1 if incompete table
+ * is given: "fixed inflate" decoder feeds us such data.
  */
+#define BAD_HUFT(p) ((uintptr_t)(p) & 1)
+#define ERR_RET     ((huft_t*)(uintptr_t)1)
 static huft_t* huft_build(const unsigned *b, const unsigned n,
                         const unsigned s, const struct cp_ext *cp_ext,
                         unsigned *m)
@@ -347,11 +353,11 @@ static huft_t* huft_build(const unsigned *b, const unsigned n,
         for (y = 1 << j; j < i; j++, y <<= 1) {
                 y -= c[j];
                 if (y < 0)
-                        return NULL; /* bad input: more codes than bits */
+                        return ERR_RET; /* bad input: more codes than bits */
         }
         y -= c[i];
         if (y < 0)
-                return NULL;
+                return ERR_RET;
         c[i] += y;
 
         /* Generate starting offsets into the value table for each length */
@@ -378,7 +384,7 @@ static huft_t* huft_build(const unsigned *b, const unsigned n,
         } while (++i < n);
 
         /* Generate the Huffman codes and for each, make the table entries */
-        result = NULL;
+        result = ERR_RET;
         t = &result;
         x[0] = i = 0;   /* first Huffman code is zero */
         p = v;          /* grab values in bit order */
@@ -472,7 +478,8 @@ static huft_t* huft_build(const unsigned *b, const unsigned n,
         *m = ws[1];
 
         if (y != 0 && g != 1) /* we were given an incomplete table */
-                return NULL;
+                /* return "result" ORed with 1 */
+                return (void*)((uintptr_t)result | 1);
 
         return result;
 }
@@ -776,13 +783,16 @@ static int inflate_block(STATE_PARAM smallint *e)
                         ll[i] = 8;
                 bl = 7;
                 inflate_codes_tl = huft_build(ll, 288, 257, &lit, &bl);
-                /* huft_build() never returns error here - we use known data */
+                /* ^^^ never returns error here - we use known data */
 
                 /* set up distance table */
                 for (i = 0; i < 30; i++) /* make an incomplete code set */
                         ll[i] = 5;
                 bd = 5;
                 inflate_codes_td = huft_build(ll, 30, 0, &dist, &bd);
+                /* ^^^ does return error here! (lsb bit is set) - we gave it incomplete code set */
+                /* clearing error bit: */
+                inflate_codes_td = (void*)((uintptr_t)inflate_codes_td & ~(uintptr_t)1);
 
                 /* set up data for inflate_codes() */
                 inflate_codes_setup(PASS_STATE bl, bd);
@@ -849,7 +859,7 @@ static int inflate_block(STATE_PARAM smallint *e)
                 /* build decoding table for trees - single level, 7 bit lookup */
                 bl = 7;
                 inflate_codes_tl = huft_build(ll, 19, 19, NULL, &bl);
-                if (!inflate_codes_tl) {
+                if (BAD_HUFT(inflate_codes_tl)) {
                         abort_unzip(PASS_STATE_ONLY);   /* incomplete code set */
                 }
 
@@ -914,12 +924,12 @@ static int inflate_block(STATE_PARAM smallint *e)
                 /* build the decoding tables for literal/length and distance codes */
                 bl = lbits;
                 inflate_codes_tl = huft_build(ll, nl, 257, &lit, &bl);
-                if (!inflate_codes_tl) {
+                if (BAD_HUFT(inflate_codes_tl)) {
                         abort_unzip(PASS_STATE_ONLY);
                 }
                 bd = dbits;
                 inflate_codes_td = huft_build(ll + nl, nd, 0, &dist, &bd);
-                if (!inflate_codes_td) {
+                if (BAD_HUFT(inflate_codes_td)) {
                         abort_unzip(PASS_STATE_ONLY);
                 }